EP0824233A2 - Procédé et appareil pour l'exécution sécurisée du logiciel avant la mise hors tension d'un ordinateur ou avant le passage de l'ordinateur dans un mode à faible consommation d'énergie - Google Patents

Procédé et appareil pour l'exécution sécurisée du logiciel avant la mise hors tension d'un ordinateur ou avant le passage de l'ordinateur dans un mode à faible consommation d'énergie Download PDF

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Publication number
EP0824233A2
EP0824233A2 EP97305891A EP97305891A EP0824233A2 EP 0824233 A2 EP0824233 A2 EP 0824233A2 EP 97305891 A EP97305891 A EP 97305891A EP 97305891 A EP97305891 A EP 97305891A EP 0824233 A2 EP0824233 A2 EP 0824233A2
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EP
European Patent Office
Prior art keywords
detection value
modification detection
secure
computer system
stored table
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Application number
EP97305891A
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German (de)
English (en)
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EP0824233A3 (fr
Inventor
Michael F. Angelo
Craig A. Miller
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Compaq Computer Corp
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Compaq Computer Corp
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Publication of EP0824233A2 publication Critical patent/EP0824233A2/fr
Publication of EP0824233A3 publication Critical patent/EP0824233A3/fr
Withdrawn legal-status Critical Current

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    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F1/00—Details not covered by groups G06F3/00 - G06F13/00 and G06F21/00
    • G06F1/26—Power supply means, e.g. regulation thereof
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F1/00—Details not covered by groups G06F3/00 - G06F13/00 and G06F21/00
    • G06F1/26—Power supply means, e.g. regulation thereof
    • G06F1/30—Means for acting in the event of power-supply failure or interruption, e.g. power-supply fluctuations
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F21/00—Security arrangements for protecting computers, components thereof, programs or data against unauthorised activity
    • G06F21/70—Protecting specific internal or peripheral components, in which the protection of a component leads to protection of the entire computer
    • G06F21/81—Protecting specific internal or peripheral components, in which the protection of a component leads to protection of the entire computer by operating on the power supply, e.g. enabling or disabling power-on, sleep or resume operations

Definitions

  • the present invention relates to computer system security.
  • the present invention relates to a method for securely executing registered software applications in a computer system that is either being powered down or entering an energy saving mode.
  • File corruption usually follows a system failure occurring during a file transfer (i.e. the system is turned off while a file is being copied onto the hard disk, etc.) or similar occurrence.
  • Controlling the power-down of the computer system is therefore important, particularly in computers with advanced operating systems such as Windows 95TM and Windows NTTM, available from Microsoft Corp. These operating systems require the user to shut down via specific software steps rather than by simply turning off the power switch. For example, in Windows 95TM, the user should click a START button and select the SHUT DOWN item from the START menu. The selection of the SHUT DOWN item causes a dialog box to appear on the screen, giving the user the options of shutting down completely, restarting the PC, or exiting to the disk operating system (DOS).
  • DOS disk operating system
  • shut down procedure is needed because the numerous pieces of status information and configuration data contained in the Windows Registry file are not updated until the system has been properly shut down. Further, data stored in the disk cache may not be flushed to the disk unless the user properly exits Windows 95TM or Windows NTTM. Network connections that are not properly severed can cause additional problems. Thus, the removal of power without following the proper shutdown procedure can corrupt the Windows Registry file and compromise the overall reliability ofthe computer during subsequent operations. It should be noted, however, that properly exiting these operating systems requires the user to take affirmative action via menu commands prior to toggling the on/offpower switch.
  • Viruses are typically designed to replicate by secretly attaching copies of themselves to files or boot records so that the user is unaware of the intrusion. It is important to note that once a virus has attached itself to a host program, the program must be different and its integrity has been violated.
  • any subsequent copies of the host file also contain the virus, thereby increasing the potential for destruction.
  • the virus is then activated when the file is executed. Consequently, a virus attached to a data file may remain dormant because the data file is not executable.
  • virus checking software One common commercial method of assessing the integrity of user software is to check for viruses by running a virus checking software program. Such programs rely on the characteristics of the known viruses to detect their presence. A new virus may not be detectable by the virus checking software. If a virus is present, the virus checking software itself is susceptible because it is loaded from the infected hard disk and must run in memory that could be infected. In addition, virus checking software can be inconvenient to execute. A thorough check of system resources can take several minutes, and the user is not able to run other applications during this time. Although virus checking software can be configured to execute automatically during system boot up, the user must again take affirmative action to execute or schedule a virus scan at other times.
  • Another method of assessing a file's integrity prior to executing involves computing an integrity assessment code for the file and verifying that the code matches a predetermined value.
  • Checksums (a type of integrity assessment code) are adequate for detecting accidental modifications of data. However, they are an insecure defense against viruses. A well-designed virus aimed at bypassing normal security features can easily attach itself to a host program without resulting in a different checksum.
  • Modification detection codes have been developed to specifically detect deliberate corruption of data, and are superior to simple checksums.
  • the intent of MDC's is to make it computationally infeasible to modify data so as to preserve a specific modification detection code value.
  • Modification detection codes are sometimes referred to by other names, including: “cryptographic checksums”, “cryptographic hashes”, “secure hash algorithms”, and “message digests”.
  • a secure hash value is calculated and stored for newly installed software. Thereafter, when the computer is turned on again, the stored hash value is compared to a newly calculated value. If a discrepancy is found, the user is alerted.
  • a main disadvantage with this method is that the integrity assessment codes must be stored on the hard disk, thus making the codes themselves susceptible to attack by malicious code. Reverse-engineering a modification detection code, while difficult, is not a mathematically intractable problem. Thus, software-only protective products can offer only limited insurance against the attack of malicious code, due mainly to architectural weakness present in most computer systems.
  • a potential solution is to embed the modification detection code in a permanent read-only memory device, but this can make system reconfiguration quite difficult.
  • Some degree of protection from data loss is afforded by performing regular backups to a tape drive or similar storage medium. If a file becomes corrupted, an earlier, trusted version can be restored from a backup tape. Any changes made to the file after the backup was performed are lost. Like virus scanning and various other administrative procedures, performing backup operations usually preempts other uses of the computer. To circumvent this potential inconvenience, it is desirable to schedule backups during non-working hours or at times when the user is away from the machine. Scheduling and running the backups also require some sort of affirmative action to be taken by the user or system administrator.
  • the present invention provides a computer system having the capability to automatically and securely execute registered commands or applications immediately prior to the computer powering down or entering a low energy consumption mode.
  • a system management interrupt is generated.
  • SMI system management interrupt
  • closure or toggling of the power supply on/off switch causes special interrupt circuitry to generate an interrupt service request that instructs the processor to jump to an interrupt service routine which results in a power down SMI being asserted.
  • circuitry coupled to the power supply on/off switch Is configured to bypass the interrupt request and generate the power down SMI directly without the need for a standard interrupt.
  • toggling the power supply on/off switch initiates a software process that results in a power down SMI.
  • a computer system also allows automatic and secure execution of registered applications immediately prior to the computer system entering a low power consumption mode.
  • Examples of such a low power consumption mode include "hibernation mode" and "energy saving mode”.
  • an SMI is again generated in one of a number of ways. Special interrupt circuitry, a keyboard interrupt, activity timers or a software process can all be used to generate the SMI.
  • the power down or hibernation mode SMI places the computer system in system management mode, causing an SMI handler routine to be executed.
  • the SMI handler responds by executing all applications registered with the application registrar. Importantly, the registered applications are verified and executed in a secure manner.
  • the SMI handler Before executing a registered application, the SMI handler first generates a current hash value for the program.
  • the term "secure hash value” or “hash value” is used throughout the remainder of this specification to refer generally to a value generated by a modification detection code, the value being specific to a given software application.
  • a "secure hash value” in the preferred embodiment is 160 bits of data (20 bytes) that is essentially a mathematical representation of a file. If any bits in the file are changed, a different hash value will result.
  • a secure hash table (or other type of integrity assessment code) is provided that contains a secure hash value for each program that the user wants to execute prior to the power down or entry into hibernation mode.
  • the hash table is stored in protected memory that can only be accessed when the computer system is in system management mode. After it has generated a current hash value for the registered application, the SMI handler checks this stored hash table for a secure entry for the application. If a hash value entry is found, it is compared with the newly-calculated hash value for the secured application. In the event the two values match, the integrity of the application is guaranteed and it is loaded into memory and executed. The process is repeated until all applications registered with the application registrar have been executed.
  • SMM memory system management mode memory
  • a secured hash value for the table is maintained in SMM memory, with the hash table itself is stored in normal memory.
  • a current table hash value is generated for the hash table before a hash table entry is accessed.
  • the current table hash value is then compared with the table hash value stored in SMM memory. If the values are equal, the integrity of the hash table is verified and the new hash value of the program to be executed can be safely compared with its original value.
  • the SMI handler transmits a shutdown command to a decoder over a system bus if the SMI was generated as a result of a power down request.
  • the decoder logic Upon detecting that the computer system has issued a shutdown command, the decoder logic causes a SHUTDOWN input to the power supply to be asserted, thereby disabling power to the system. If the SMI was generated as a result of low power consumption mode being activated, the SMI handler transmits appropriate commands to hibernation logic that controls various system components.
  • the present invention has a wide variety of potential applications, including secure execution of virus detection and removal programs and backing up files prior to shutting down. These and other registered applications are executed securely and without need for intervention by the user.
  • a computer system S incorporates two primary buses: a Peripheral Component Interconnect (PCI) bus P which includes an address/data portion and a control signal portion; and an Industry Standard Architecture (ISA) bus I which includes an address portion, a data portion, and a control signal portion.
  • PCI Peripheral Component Interconnect
  • ISA Industry Standard Architecture
  • a CPU/memory subsystem 100 is connected to the PCI bus P.
  • the processor 102 is preferably the Pentium® processor from Intel Corporation, but could be an 80486 or any number of similar or next-generation processors.
  • the processor 102 drives data, address, and control portions 116, 106, and 108 of a host bus HB.
  • a level 2 (L2) or external cache memory 104 is connected to the host bus HB to provide additional caching capabilities that improve the overall performance of the computer system S.
  • the L2 cache 104 may be permanently installed or may be removable if desired.
  • a cache and memory controller 110 and a PCI-ISA bridge chip 130 are connected to the control and address portions 108 and 106 of the host bus HB.
  • the cache and memory controller chip 110 is configured to control a series of data buffers 112.
  • the data buffers 112 are preferably the 82433LX from Intel, and are coupled to and drive the host data bus 116 and a MD or memory data bus 118 that is connected to a memory array 114.
  • a memory address and memory control signal bus is provided from the cache and memory controller 110.
  • the data buffers 112, cache and memory controller 110, and PCI-ISA bridge 130 are all connected to the PCI bus P.
  • the PCI-ISA bridge 130 is used to convert signals between the PCI bus P and the ISA bus I.
  • the PCI-ISA bridge 130 includes: the necessary address and data buffers, arbitration and bus master control logic for the PCI bus P, ISA arbitration circuitry, an ISA bus controller as conventionally used in ISA systems, an IDE (intelligent drive electronics) interface, and a DMA controller.
  • a hard disk drive 140 is connected to the IDE interface of the PCI-ISA bridge 130. Tape drives, CD-ROM devices or other peripheral storage devices (not shown) can be similarly connected.
  • the PCI-ISA bridge 130 also includes miscellaneous system logic.
  • This miscellaneous system logic contains counters and activity timers as conventionally present in personal computer systems, an interrupt controller for both the PCI and ISA buses P and I, and power management logic. Additionally, the miscellaneous system logic may include circuitry for a security management system used for password verification and to allow access to protected resources.
  • the PCI-ISA bridge 130 also includes circuitry to generate a "soft" SMI (System Management Interrupt), as well as SMI and keyboard controller interface circuitry.
  • the miscellaneous system logic is connected to the flash ROM 154 through write protection logic 164.
  • the PCI-ISA bridge 130 is a single integrated circuit, but other combinations are possible.
  • a series of ISA slots 134 are connected to the ISA bus I to receive ISA adapter cards.
  • a series of PCI slots 142 are similarly provided on the PCI bus P to receive PCI adapter cards.
  • a video controller 165 is also connected to the PCI bus P.
  • Video memory 166 is used to store graphics data and is connected to the video graphics controller 165 and a digital/analog converter (RAMDAC) 168.
  • the video graphics controller 165 controls the operation of the video memory 166, allowing data to be written and retrieved as required.
  • a monitor connector 169 is connected to the RAMDAC 168 for connecting a monitor 170.
  • a network interface controller (NIC) 122 is also connected to the PCI bus P.
  • the controller 122 is a single integrated circuit that includes the capabilities necessary to act as a PCI bus master and slave, as well as circuitry required to act as an Ethernet interface.
  • Attachment Unit Interface (AUI) and 10 base-T connectors 124 are provided in the system S, and are connected to the NIC 122 via filter and transformer circuitry 126. This circuitry forms a network or Ethernet connection for connecting the computer system S to a local area network (LAN).
  • LAN local area network
  • a combination I/O chip 136 is connected to the ISA bus I.
  • the combination I/O chip 136 preferably includes a real time clock two UARTS, a floppy disk controller for controlling a floppy disk drive 138, and various address decode logic and security logic to control access to the CMOS memory (not shown) and power-on password values.
  • a control line is provided to the read and write protection logic 164 to further control access to the flash ROM 154.
  • Serial port connectors 146 and parallel port connector 132 are also connected to the combination I/O chip 136.
  • An 8042 or keyboard controller is also included in the combination I/O chip 136.
  • the keyboard controller is of conventional design and is connected in turn to a keyboard connector 158 and a mouse or pointing device connector 160.
  • a keyboard 159 is connected to the computer system S through the keyboard connector 158.
  • a buffer 144 is connected to the ISA bus I to provide an additional X-bus X for various additional components of the computer system S.
  • a flash ROM 154 receives its control, address and data signals from the X-bus X.
  • the flash ROM 154 contains the BIOS information for the computer system and can be reprogrammed to allow for revisions of the BIOS.
  • a regulated power supply 180 In the computer system S of Fig. 1, all electronic devices discussed above, including the processor 102, are powered by a regulated power supply 180.
  • the regulated power supply (Figs. 3 and 4) has a power supply supervisory circuit 192 that provides shutdown capability via a SHUTDOWN input.
  • the power supply 180 is shut-down via an SMI software/hardware process that is initiated by toggling the on/off switch 182 (Fig. 3).
  • the power supply 180 receives an AC voltage supply via an AC plug 190 (Fig. 3).
  • SMM System Management Mode
  • SMM system management mode
  • SMI system management interrupt
  • Intel Corporation a mode referred to as system management mode
  • SMIs were power management interrupts devised by Intel Corporation for portable systems. Portable computers often draw power from batteries which provide a limited amount of energy. To maximize battery life, an SMI is typically asserted to turn off or reduce the power to any system component that is not currently in use. Although originally meant for laptop computers, SMIs have become popular for desktop and other stationary models as well.
  • SMIs are asserted by either an SMI timer, by a system request, or by other means.
  • An SMI is a non-maskable interrupt having almost the highest priority in the system. Only the reset signal R/S* and cache flush signal FLUSH*, which can be conceptualized as interrupts, have a higher priority than the SMI.
  • SMM memory system management mode memory
  • an SMI handler routine which is an interrupt service routine to perform specific system management tasks such as reducing power to specific devices or, as in the case of the present invention, providing security services. While the routine is executed, other interrupt requests are not serviced, and are ignored until the interrupt routine is completed or the microprocessor is reset.
  • SMI handler completes its task, the processor state is retrieved from the SMM memory, and the main program continues.
  • An SMI active signal referred to as the SMIACT* signal is provided by the processor to indicate operation in SMM.
  • the processor 102 calls the SMI handler, which addresses an address space that is separate from ordinary main memory. Thereafter, all memory accesses refer only to SMM memory 200. Input/output ("I/O") accesses via instructions such as IN or OUT are still directed to the normal I/O address space, however.
  • I/O Input/output
  • One advantageous side-effect of the hardwired separate address SMM area is that the routines stored in this space cannot be snooped by the cache, providing an additional layer of protection.
  • SMIACT* signal is at a logic low level
  • SMIACT* signal is at a logic high level
  • the Pentium®, or P5, microprocessor is more flexible than earlier processors in that it permits the SMI handler starting address and the location of the SMM memory space to be changed by the user.
  • the SMI starting address stored in the microprocessor register is initially set to the conventional 30000h value. Consequently, when the first SMI is asserted, the SMI handler starts at address 38000h (the entry point is offset from the SMM memory base). While the SMI handler routine is executing, however, it may provide a different area of memory to be used as the SMM memory. This new SMM memory may start at any location in the main memory space chosen by the programmer.
  • the SMM memory is a 64-Kbyte block beginning at the new SMM memory start address. When the SMI handler finishes, the new starting address replaces the old starting address in the microprocessor's SMI starting address register.
  • the microprocessor maps the new 64-Kbyte block of memory into the main memory space as the SMM memory, and starts the SMI handler at the new starting address at the midpoint of the new SMM memory. For example, during the first SMI service routine, the programmer may change the SMM memory starting point from 030000h to 100000h.
  • the microprocessor maps the SMM memory into main memory space between 100000h and 10FFFFh. The microprocessor then references address 108000h for the SMI handler. This feature thus allows the programmer to choose a more convenient location in the main memory.
  • FIG. 2 a graphical representation of SMM memory 200 as configured according to the present invention is shown. As mentioned above, this address space is addressed by the processor 102 following an SMI. Following an SMI, the state of the processor 102 is stored in the CPU register dump 210. The SMI handler 201 is then called and executed by the processor 102. Importantly, the SMI handler 201 can be written such that it performs tasks other than power-down operations.
  • An SMI handler 201 written according to the present invention is able to utilize an application registrar 202, stored hash entries 204, a stored hash table 206, and a secure hash algorithm 208 to securely register and verify the integrity of software applications prior to execution.
  • SMM memory 200 is only addressable while the computer system is in SMM, storing the application registrar 202, the hash entries 204, the hash table 206 and the secure hash algorithm 208 in SMM memory 200 prevents malicious code from modifying or reading these sensitive components of the preferred embodiment of the invention.
  • a secured table hash value for the hash table 206 itself is maintained in SMM memory 200, while the hash table 206 is stored in normal, readable memory.
  • the integrity of the hash table 206 is verified before the hash value of the program to be executed is compared with its original value.
  • This embodiment of the invention discussed more fully below, is useful for overcoming problems associated with the limited size of SMM memory (64-Kbyte total in the disclosed embodiment).
  • the secure hash algorithm 208 could be stored in flash ROM 154.
  • the optional 32-Kbyte SMM RAM extension 212 can be utilized for secure execution of software or to store additional hash values.
  • secure hash value or “hash value” refers generally to a value -- generated by an integrity assessment code -- that is specific to a given software application.
  • hash table 206 containing hash values generated by a secure hash algorithm 208, it is contemplated that many types of modification detection codes could be utilized.
  • modification detection codes Of importance to the invention is that each piece of registered software has a corresponding and distinct value that represents the unaltered state of the software, and that this value be stored in a secure memory location.
  • registered software is referred to generally as “programs” or “applications”, and use of these terms is intended to cover software "files”.
  • the interrupt controller/SMI generation logic 186 receives an input from a power supply on/off switch 182. One end of the on/off switch 182 is connected to ground, while the other end of the on/off switch 182 is connected to a pull-up resistor 184. The output of the on/off switch is connected to the interrupt controller/SMI generation logic 186.
  • the power supply on/off switch 182 is closed -- indicating that the user desires to power the system down -- the input to the interrupt controller/SMI generation logic 186 is pulled low. While the on/off switch 182 is open, pull up resistor 184 pulls the input to a high logic level.
  • the outputs of the interrupt controller/SMI generation logic are placed onto the primary PCI bus P for transmission to the processor 102.
  • an SMI is communicated between the interrupt controller/SMI generation logic 186 and the processor 102.
  • the interrupt controller/SMI generation logic 186 is preferably contained within the PCI-ISA bridge 130, although it could be located elsewhere within the system.
  • the interrupt controller/SMI generation logic 186 can be configured to generate a special interrupt request.
  • the interrupt request instructs the processor 102 to jump to an interrupt service routine which results in a power down SMI being asserted.
  • the SMI handler 201 responds by executing all applications which are registered with the application registrar 202. After the registered applications have been executed, the SMI handler 201 transmits a shut down command to a decoder 188 over the PCI bus P.
  • the decoder logic 188 Upon detecting that the computer system S has issued a shutdown command, the decoder logic 188 causes the SHUTDOWN input to the power supply 180 to be asserted, thereby disabling power to the system.
  • the interrupt controller/SMI generation logic 186 can be configured to bypass an interrupt request and generate an SMI directly without the need for a standard interrupt.
  • information is first written to an appropriate register to communicate a power down request to the SMI handler 201.
  • toggling the power supply on/off switch 182 initiates a software process that results in a power down SMI.
  • Additional hardware and software mechanisms are capable of being modified to generate a power down SMI. These methods include the ability to write to a pre-defined I/O port using the Automatic System Management Interrupt (ASMI) mechanism that results in an SMI.
  • ASMI Automatic System Management Interrupt
  • Other methods are also described in programmer's reference manuals (such as the "Inte1486TM SL Microprocessor SuperSet Programmer's Reference Manual") for processors that incorporate system management mode capabilities, and are not detailed here for sake of clarity.
  • the output of the decoder logic 188 can be used to cause a switch 189 to break the connection between the alternating current (AC) line input ofthe power supply 180.
  • a first end of the AC plug 190 is connected to one end of the switch 189, while a second end of the plug 190 is connected to a second AC input of the power supply 180.
  • a second end of the switch 189 is connected to the first AC input of the power supply 180.
  • the switch 189 can be further connected to the output of the power supply on/off switch 182 so that the connection between the AC plug 190 and the power supply 180 is restored when the user moves the on/off switch 182 to turn on the computer system S from a power down condition.
  • the switch 189 normally provides and electrical connection for the AC voltage from the plug 190 to the power supply 180.
  • the decoder logic 188 upon receipt of a shutdown instruction sent by the processor in response to an SMI from the interrupt controller/SMI generation logic 186, passes the shutdown instruction in the form of an ACTUATION signal (not shown) to the switch 189.
  • the assertion ofthe ACTUATION signal causes the switch 189, which can be electronic or electro-mechanical (including power FETs, relays or solid state relays) to be actuated. This in turn breaks or completes the electrical connection between the AC plug 190 and power supply 180.
  • the switch 189 upon receipt of the shutdown command by the processor 102 after the power supply on/off switch 182 is toggled, the switch 189 disables the power supply 180 so that the system can be powered down following secure execution of registered applications.
  • the processor 102 could periodically poll the power supply on/off switch 182 to sense shutdown requests, the preferred embodiment of the present invention contemplates the use of an interrupt approach.
  • the interrupt approach is more efficient because it allows the processor 102 to execute its main programs and to service peripheral devices such as the on/off switch 182 only when service is requested by the device itself. In the preferred embodiment, therefore, closure of the power supply on/off switch 182 generates an interrupt signal to the interrupt controller/SMI generation logic 186. An interrupt is then generated that is serviced by an interrupt service routine that results in an SMI.
  • the interrupt controller 186 coupled to the PCI bus functions as an overall manager in accepting interrupt requests from I/O devices.
  • the interrupt controller 186 receives interrupts at selected, assigned inputs from devices located on the expansion bus as well as within the enclosure, including the interrupt signal from the power supply on/off switch 182.
  • the interrupt controller 186 On receipt of the interrupt signal from the power supply on/off switch 182, the interrupt controller 186 pulses an interrupt input to the processor 102.
  • the processor completes the currently executing instruction, issues an interrupt acknowledge signal to the interrupt controller 186, and then executes a service routine to service the requesting device.
  • the processor writes an End-of-Interrupt (EOI) input/output (I/O) command to the interrupt controller and continues processing where it left off.
  • EOI command is typically sent through an I/O instruction to a register within the interrupt controller 186.
  • the interrupt controller 186 responds to the assertion of an interrupt acknowledge signal from the processor 102 by providing the appropriate interrupt vector to the PCI bus P.
  • the interrupt vector points to the address of an interrupt service routine that results in a shutdown SMI.
  • the interrupt service routine is then executed. Since the processor 102 of the computer system S need not poll the on/off switch 182, detection of the user's request for turning off the computer system S via the on/off switch 182 can be performed using minimal computing resources.
  • the internal circuitry of the regulated power supply 180 is shown in Fig. 4.
  • the circuitry includes a conventional power converter 196 for converting an AC voltage to one or more DC voltages.
  • the power converter 196 preferably has a pair of input power terminals connected to a single-phase AC input power source via the plug 190.
  • the AC terminals are coupled across a bridge rectifier arrangement which develops a high DC voltage across a filter capacitor.
  • This high DC voltage is connected to the input of a power supply controller 194 that includes a pulse width modulator (PWM) for converting the high DC input voltage to a low DC output voltage.
  • PWM pulse width modulator
  • the output of the power converter 194 is also connected to a power supply supervisory circuit 192 which generates various output signals indicating the state of the power supply 180, including a POWERGOOD signal.
  • the power supply supervisory circuit 192 also receives the shutdown signal input SHUTDOWN which functions to disable the power supply 180. As has been disclosed, the SHUTDOWN input is asserted following secure execution of the applications registered with the application register 202.
  • the PWM controller 194 operates as a fixed frequency current mode controller where the duty cycle is set by the input/output voltage ratio.
  • the PWM controller 194 has an enable/disable input signal, driven by a signal from the power supply supervisory circuit 192.
  • the pulse width modulator 194 can thereby be disabled to shutdown the power supply 180 following the secure shutdown procedure.
  • hibernation circuitry for generating an SMI prior to the system entering energy saving mode is shown.
  • Such an energy saving mode is normally entered when the computer system has not been used for a predetermined period of time. The user is presumably not using the computer for other tasks at this point in time.
  • Running registered processes such as file backups, virus scans and disk defragmentation programs prior to the computer system S entering energy saving mode is therefore advantageous.
  • a method for execution of the registered applications is discussed more fully in conjunction with Fig. 6.
  • Entry into energy saving mode can be predicated on a number of events occurring, including: video or disk drive inactivity, keyboard commands, or SMI countdown timers (which are preferably made visible to other system processes).
  • SMI countdown timers which are preferably made visible to other system processes.
  • Various warning timers are provided in processors incorporating system management mode capabilities. These timers can be programmed to allow the system to finish I/O operations such as DMA and disk accesses before the actual SMI is generated.
  • a hard drive 140 and monitor 170 are used as examples of devices whose inactivity can trigger energy saving mode.
  • Video and disk I/O activity timers 197 are used to monitor the PCI bus P for activity occurring on the hard drive 140 and the monitor 170. Following a period of inactivity of predetermined length, the video and disk I/O activity timers 197 communicate a signal to the interrupt controller/SMI generation logic 186'.
  • the interrupt controller/SMI generation logic 186' operates in a similar fashion to the interrupt controller/SMI generation logic 186 of Fig. 3.
  • the interrupt controller 186' responds by asserting an interrupt request which is eventually acknowledged by the processor 102.
  • the interrupt request eventually results in an execution of an interrupt service routine followed by assertion of an SMI to the processor 102.
  • commands are sent over the PCI bus P instructing the hibernation logic 199 to enter energy saving mode.
  • hibernation logic block 199 responds by asserting a signal SPIN_DOWN to the hard drive 140 which results in the hard drive "spinning down" its internal storage platters.
  • SPIN_DOWN a signal which is preferably ENERGY STAR compliant
  • STANDBY is received from the hibernation logic 199.
  • Energy saving mode can also result in the processor 102 and other system components being clocked at a lower frequency in order to reduce power consumption.
  • video and disk I/O activity timers 197 could be replaced by a software process that monitors activity to peripheral devices such as the hard drive 140 and monitor 170.
  • the contemplated software monitors the system bus for different types of events (i.e., interrupts for hardware devices, I/O writes, etc.). If one of these events occurs within a specified amount of time, a software timer is reset and no action is taken. If inactivity exceeds a predetermined amount of time, various "levels" of hibernation mode can be entered. For example, the monitor 170 can be powered down followed by power down of the hard drive 140 if a second set of events does not occur within a second predetermined amount of time. This embodiment of the invention results in a considerably reduced gate count.
  • a suitable SMI can be generated at any point in the process, followed by execution of registered applications.
  • the SMI is generated by a software polling process that polls standby signals.
  • the video or disk standby signals can be generated by the aforementioned timers or by other means.
  • the polling process generates an SMI after it determines that a specified system component (such as the monitor 170 or hard drive 140) has entered standby as indicated by its associated standby signal.
  • hibernation mode is entered as a result of a special keyboard interrupt.
  • the interrupt controller/SMI generation logic 186' is programmed to respond to the special keyboard interrupt by asserting an interrupt request that results in generation of an SMI and execution of the registered applications prior to hibernation.
  • Fig. 6 a flow chart illustration is provided for a method according to the present invention for securely executing registered applications prior to power down or hibernation mode is shown.
  • Control commences in step 300 where either the power supply on/off switch 182 is toggled, or a condition occurs which enables an energy saving mode.
  • Control proceeds to step 302 where an SMI is generated and the processor 102 enters system management mode as a result of the SMI.
  • the circuitry of Figs. 3 and 5 are demonstrative of methods for generating the SMI, but it is contemplated that the SMI could be generated by a variety of "interrupt generators".
  • the system management capabilities incorporated in Intel Corp. processors are referred to as "system management mode". Other manufacturers may refer to similar system management capabilities by different names. Of importance to the present invention is a protected address space accessible (preferably in real time) while the processor is in a system management-type mode.
  • the SMI that is generated in step 302 causes an SMI handler 201 to be executed. Execution of the SMI handler 201 is operating system independent. Control next proceeds to step 306 where the SMI handler 201 examines the application registrar 202 to determine if registered programs have yet to be executed. Any type of program, including system administration type applications, can be executed. Prior to a power down or energy saving mode, the invention can also be utilized to gracefully shut down the operating system by flushing file buffers to disk and sending a close signal to each open Wmdows application (applet) and/or other running processes. Data loss due to an accidental or premature removal of power is thereby avoided.
  • step 308 Ifa program is to be executed as determined in step 306, control passes to step 308 where the SMI handler 201 requests a secure hash value for the program to be executed.
  • This secure hash value is typically generated by the secure hash algorithm 208.
  • Control then passes to step 310 to validate the stored hash table 206 if it is not stored in SMM memory 200. Validation of the stored hash table 206 is accomplished by first generating a current table hash value for the hash table 206 itself. This new table hash value is then compared with a secured table hash value for the hash table 206. If the two values match, the integrity of the hash table 206 is verified.
  • This step allows the hash table 206 to be stored in normal memory, thereby allowing a portion of SMM memory 200 to be used for other purposes, such as secure execution of an application. Note that any authorized modifications to the hash table 206 must be reflected in an updated secure table hash value. If the hash table 206 is stored in SMM memory 200, step 310 is not required because the hash table 206 is presumptively secure.
  • the SMI handler 201 next determines if the hash table 206 contains a hash value corresponding to the registered program to be executed. Typically, a secure hash value is created for each program and added to the hash table 206 at the same time the application is added to the application registrar 202. If a hash value for the program is found, control proceeds to step 314 where the stored hash value is retrieved. Control then proceeds to step 314 for a comparison of the newly generated hash value with the stored hash value. If the two values are the same, control passes to step 318 and the program is loaded into memory and executed. As mentioned, the program or portions of it can be loaded into the SMM memory 200 for execution.
  • the program can be executed from normal memory if secure execution is not needed. In the latter case, system management mode can be exited prior to execution of the program, followed by a return to system management mode after completion of the program. In either case, control returns to step 306 to determine if there are any registered programs that have not been executed.
  • step 312 if no hash value corresponding to the program to be executed is found, control proceeds to step 320 and the user is informed that the program is not properly registered to be executed. Control then proceeds to step 322, which is also where control proceeds if the stored hash value does not equal the newly calculated hash value as determined step in 316 (for example, the program has been modified by a virus or a new version ofthe program has been installed).
  • step 322 which is an optional enhancement to the present invention, the system is configured to query the user to update the hash table 206 and/or stored hash value to incorporate the program as it currently exists. Alternatively, the user could simply be asked for permission to run the program in its altered state.
  • a flow chart illustration of a secure method UPDATE 400 for updating a stored hash table or stored hash value is shown.
  • entries can be deleted for programs that are no longer utilized.
  • the subroutine UPDATE 400 is called in step 324 of Fig. 6.
  • an initial step 401 the system determines if an administrative password is required to update the stored hash table or stored hash value. If so, the user is prompted for an "administrative" password. The computer system may leave system management mode while the user is entering the administrative password, although entry of the password may not be entirely secure. An SMI is then generated and the computer system enters system management mode in step 404. Control then proceeds to step 406 and a one-way hash value is generated for the entered password. Proceeding to step 408, this hash value is then compared with a hash value stored in SMM memory 200.
  • control proceeds to step 412 and the hash table and/or stored hash values are updated according to the user's instructions. Control also passes to step 412 if an administrative password is not required as determined in step 401. If the hash values do not match as determined in step 410, control passes to step 414 and the user is informed of the discrepancy. In either case, control next proceeds to step 416 for a return to the main routine of Fig. 6.
  • a secure keyboard link to a "black box" security device integrated within a system component such as the PCI-ISA bridge 130.
  • the password data as well as user-entered keystrokes are not stored in normal readable memory, preventing them from being surreptitiously obtained.
  • the secured keyboard link is initiated by the SMI handler and each keystroke is sent to the black box while the system is in SMM.
  • the keystrokes are not visible to any other processes, and the black box can only be written in this manner. It is contemplated that this method can be used to enter an administrative password required to update the secured hash table.
  • a computer system provides for automatically and securely executing registered programs immediately prior to the computer system powering down or entering an energy saving mode.
  • An SMI is generated that causes an SMI handler routine to generate current hash values for registered programs.
  • the new hash values are securely compared with stored hash values prior to execution of the programs.
  • the system automatically powers down or enters a reduced energy consumption mode.
  • the present invention thereby allows secure and convenient execution of programs or commands that would typically interfere with normal computer use.

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EP97305891A 1996-08-07 1997-08-04 Procédé et appareil pour l'exécution sécurisée du logiciel avant la mise hors tension d'un ordinateur ou avant le passage de l'ordinateur dans un mode à faible consommation d'énergie Withdrawn EP0824233A3 (fr)

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